You can help to prevent wear-and-tear injuries from any type of exercise by warming up, by stopping exercise when you feel pain and by not exercising intensely when your muscles feel heavy or sore. Muscles are made of millions of individual fibers. When you first contract a muscle, you use only one percent of the fibers. As you continue to exercise, you contract more fibers to share the load, which places less force on each fiber and helps to prevent injuries. Always warm up. Go slow before you go fast. If you take a hard workout and feel sore the next day, go easy on every day that your muscles continue to feel sore after you have warmed up. It usually takes at least 48 hours for muscles to recover from hard exercise. When you feel pain in one muscle during exercise, that's a signal that it may be starting to tear and you should stop exercising for that day.

Runners Get More Injuries
If you think that football is the sport with the most injuries, you are wrong. Each year, 79.3 percent of long-distance runners suffer injuries that force them to take time off from running (Br J Sports Med, Aug, 2007;41(8):469-80). The most-injured part is the knee and the chance for an injury increases with running longer distances and having previous injuries. Injuries occur most often after a rapid increase in weekly distance, intensity, or frequency of hill or track workouts (Sports Med, 1996. Jan;21(1):49-72).

A survey of participants in a Rotterdam marathon found that:
• 55 percent of the runners had suffered serious injuries during the year before the marathon
• 15.6 percent of the runners reported at least one new lower extremity injury in the month before the race
• 18.2 percent reported injuring their legs during the marathon
• Immediately after the marathon, runners reported severe pain in two to four different parts of their legs
• One week later, most felt well enough to go back to work, even though almost all had painful muscles (Scand J Med Sci Sports, April, 2008;18(2):140-4).

Why Running Causes So Many Injuries
When you run, one foot is always off the ground, so each foot strikes the ground with a force equal to three times body weight (at 6-minute-mile pace) and the faster you run, the greater the force of each foot strike. Walking is much safer. When you walk, you always have one foot on the ground, so the force of a walking foot strike almost never exceeds your body weight. To convince yourself, place your hands on the huge quad muscles in the front of your upper leg while you run. Each time your leg strikes the ground, you will feel the muscle shake like jelly.

A study from the University of Wisconsin-La Crosse shows that as people start to feel tired during running, they shorten their strides and this decreases the force of their foot striking the ground (Medicine and Science in Sports and Exercise, Dec 1999;31(12):1828-33). The shorter stride lessens the force of their heel striking the ground and places it forward to the area behind the big toe. To compensate for the decreased force of their feet hitting the ground, they move their legs at a faster cadence. You can use this information to help you prevent injuries when you run. Shortening your stride will help to protect you from injuries by shifting your foot strike force forward. You can keep your speed by moving your legs at a faster cadence.

When You Need To Take a Day Off
The most common cause of injuries is not listening to your body when it talks to you. Every wear-and-tear injury you have had probably gave you signals long before you were injured. Most exercisers who are training properly have sore muscles every day when they wake up in the morning. However as they start to exercise, the soreness goes away and their muscles feel good. On days when your muscles do not feel better after you start to exercise, take the day off. If you are exercising and you feel discomfort in one or more non-symmetrical areas, stop exercising and take the day off. Pain in one area, such as a leg, and no discomfort in the other leg, is a strong warning of impending injury that could still be prevented.

Understanding How to Train Helps to Prevent Injuries
I think it is unwise to do the same workout at the same intensity every day because:
• it will not give you the same health benefits as a stress/recover training program,
• it will not make you a better athlete,
• it may increase your chances of injuring yourself,
• it will not help you to lose as much weight as you may want, and
• it makes no sense.

To strengthen your heart and increase your ability to take in and use oxygen, you have to exercise intensely enough to feel muscle burning and become somewhat short of breath. That stresses your muscles also. To make a muscle stronger, you need to exercise vigorously enough to damage it. You go a little faster on one day, damage the muscles and feel sore on the next day. This delayed-onset muscle soreness (DOMS) is evidence that you have damaged muscles. The soreness is a sign that you should spend that day exercising at a more relaxed pace and not put much pressure on your healing muscles.

In a stress/recover training program, you should set up your schedule to go a little faster with more intensity on one day, feel sore on the next day and go at low intensity for that day and as many additional days as it takes for the soreness to go away. Then, when the soreness is gone, you exercise more intensely again.

Arches and Running Injuries
Runners with high arches are at increased risk for suffering stress fractures, small cracks in the bones of their feet and lower legs. Those with low arches are at increased risk for knee cap pain. Your legs are shocked by the force of each foot hitting the ground, and the faster you run, the harder your foot strikes the ground. This force can break bones, damage joints and tear muscles. To protect yourself from this tremendous foot-strike force, your leg is designed so that you never are supposed to land flat-footed when you run. Almost all people land on the outside (lateral) bottom of the foot and roll inward toward the medial side where the big toe is. This is called pronation and helps to distribute the force of your foot strike throughout your foot and leg and protect you from injury. The further you roll inward, the greater the protection against this force. However, when you roll in too much, your lower leg twists inward excessively, causing your kneecap to rub against the long femur bone behind it and cause pain. Pain behind the kneecap is called Runner's Knee which is one of the most common running injuries.

If you have pain behind the knee cap during running or walking, ask your podiatrist to look at your feet. If your arches appear to be flat, you usually will have a normal arch, but you roll inward so far that your arch touches the ground. Flat feet usually means that your foot rolls inward so far that the arch rolls all the way to touch the ground. If you have flat feet and no pain, you do not need to do anything. However if you have pain anywhere from your feet all the way up to your lower back, the treatment is to place special inserts called orthotics in your running shoes. You can also do special exercises that strengthen your vastus medialis muscle that pulls your knee cap inward.

If you develop pain in the medial side of your lower leg or your feet, your podiatrist will probably order a bone scan to check for stress fractures, small cracks in the bones of your feet. If you have stress fractures, you should stop running for a while and ride a bike, which causes no road shock. When you can run without feeling pain, you can start running again, but you should take shorter strides to decrease the force of your foot striking the ground. If you have high arches, you probably are not pronating enough to reduce the force of your foot strike. You can reduce the force of your foot strike by shortening your stride.

Strengthening Muscles Helps to Prevent Injuries
A study from Sweden showed that pre-season strength training for the hamstring muscles helped to prevent injuries to those muscles (Scandinavian Journal of Medicine & Science in Sports, 2003;13(4):244-250). Hamstring tears are very common soccer injuries, so players from two of the best soccer teams in Sweden were divided into two groups: a group that received specific hamstring training for 10 weeks, using a special device twice a week to overload the hamstrings eccentrically, and a control group that received no special training. The trained group had less than one third the hamstring injuries and also had greater improvement in hamstring strength and running speed. Muscles are injured when the force on them is greater than their inherent strength, so they tear. Resistance training makes muscles stronger so that they can withstand greater forces and therefore helps prevent injuries. On the other hand, stretching has not been shown to prevent muscle injuries.

My Recommendations
• Do not do the same exercise at the same intensity every day. Use the hard/easy principle: faster on one day and much slower on the next.
• Always go much slower for several minutes before you go faster.
• If your muscles do not feel fresh after you have warmed up for a few minutes, take the day off.
• Stop exercising immediately if you feel pain in one area that worsens with exercise.
• Whatever your sport, understanding the principles of training helps to prevent injuries.

Caution: Almost everyone should exercise. Check with your doctor before you start a new exercise program or increase the intensity of your existing program. Blocked arteries leading to your heart can cause a heart attack during exercise.

About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities.
Read More